1. Field of Invention
The present invention concerns a mechanical safety cover interlock for an injection-molding machine for the processing of plasticizable masses, e.g. plastic materials, pulverized and ceramic masses and, in particular it concerns a control device for interrupting the operation of the machine as soon as a protective device is moved from its protecting position. Such a machine includes a stationary mold carrier; a clamping unit; a movable mold carrier which can be moved by the clamping unit in an axial direction parallel to a mold closing direction of the machine from and to a position of interlock with the stationary mold carrier; a mold clamping area extending between the movable mold carrier and the stationary mold carrier in which parts of a mold can be fixed on the movable mold carrier or the stationary mold carrier; a support element, arranged behind the movable mold carrier as seen from the stationary mold carrier, for supporting the clamping unit for the movable mold carrier; force transmission elements for transmitting forces occurring in a closed position from the stationary mold carrier to the support element and thus to the movable mold carrier; a protective device that covers the mold clamping area while in a protecting position and which is movable in the axial direction; a locking rod extending in the axial direction and including a blocking segment; a mechanical block mechanism operating jointly with the blocking segment of the locking rod and including blocking means for blocking movement of the movable mold carrier by engagement with the blocking segment, the blocking means being movable counter to the force of an elastic means to be in a non-blocking position and, when located in the non-blocking position, being movable relative to the locking rod during a movement of the movable mold carrier; and a control device which positively engages the blocking means with the blocking segment of the locking rod when the protective device is moved from the protecting position and which permits the movement of the locking rod relative to the blocking mechanism when the protective device is in the protecting position.
2. Description of the State of the Technology
Injection-molding machines, especially plastic injection-molding machines, principally require a protective covering or protective device, which covers the mold clamping area to prevent, in particular, injuries to the operating personnel, e.g. caused through inadvertently reaching into the mechanical safety cover interlock while it is in the process of closing. When the protective device is not in the protecting position, the control circuit for the mechanical safety interlock is frequently opened so that a closing of the mold is no longer possible. In many cases, the hydraulic circulation for the mechanical safety cover interlock is also interrupted dependent upon the movement of the protective device, so that there is no danger to the operator, even if the switching unit for opening the control circuit malfunctions. A blocking mechanism for the mechanical safety cover interlock then ensures that if these safety precautions fail, a closing of the mold is no longer possible by virtue of an additional, separate safety system.
Mechanical safety cover interlocks of the above-outlined type are known, for example, from the U.S. Pat. Nos. 4,340,346 and 4,373,890. These mechanical safety cover interlocks comprise forcibly controlled, purely mechanical blocking mechanisms for the mold closing movement, having at least one locking rod attached to the movable mold platen and extending parallel to the closing direction. The locking rod extends through a bore in a platen located adjacent to the movable mold platen. There, a blocking mechanism is provided, which operates jointly with the locking rod by means of a control rod for the protective cover. However, these mechanical safety cover interlocks cannot detect, whether the blocking mechanism is in fact working, as only the position of the protective cover is detected.
U.S. Pat. No. 4,373,890 discloses locking jaws which permit an engagement at any time with the locking rod having annular ribs. For this purpose, the engagement elements on the locking jaws are displaced against each other in the direction of the locking rod. The positioning of the locking jaws occurs by means of a control element acting jointly with control wheels. As a result of a profile change in the control element, the control wheels are forced toward the outside, resulting in a movement of the two locking jaws with the assistance of transfer levers. A plurality of springs are used for the resetting. The control element is articulated, so that it is of no significance as to which part of the locking jaw first engages in the locking rod.
U.S. Pat. No. 4,382,763 discloses a mechanical safety cover interlock which does not only mechanically block the movement of the mold closing unit, but it also provides electronic signal detecting, whether the protective cover is in the protecting position. However, this electronic signal is only used to shut down the mold closing unit. Nevertheless, the possibility would exist, that the mechanical blocking mechanism is not working properly, so that a risk for the user would still exist, as the function of the blocking mechanism itself is not tested.